ORGANS OF DIGESTION. 



129 



tains the food in the small intestine until the nutriment 

 is absorbed (Fig. 58). 



The colon, extending from the cecum to the rectum, is 

 composed of the ascending, trans- 

 verse, and descending parts. The as- 

 cending colon lies on the right side; 

 the transverse extends crosswise, con- 

 necting the ascending with the de- 

 scending, which lies on the left side. 

 The descending colon terminates in 

 the rectum, which is five or six centi- 

 meters long. 



The wall of the alimentary canal is 

 composed of three chief coats- 

 mucous, areolar, and muscular. These 

 coats may be seen by cutting trans- 

 versely, with a sharp scalpel, a portion 

 of the stomach hardened in formalin. 

 The mucous coat (Fig. 60) lines the 

 lumen and contains the numerous 

 glands which vary much in the differ- 

 ent portions of the canal. The esopha- 

 gus contains the esophageal glands, 

 whose secretion probably has no other 

 effect on the food than to facilitate its 

 passage. The mucous coat of the 

 stomach contains the gastric glands, 

 which yield pepsin and hydrochloric 

 acid, the chief agents of the gastric 

 digestive fluid (Fig. 61). The glands 

 in the cardiac end of the stomach 



differ from those in the pyloric end in containing numerous 

 parietal or acid cells which probably secrete the hydro- 

 chloric acid for digestion. 



dT 



FIG. 61. - - A CROSS- 

 SECTION OF THE Mu- 

 cous COAT OF THE 

 STOMACH BETWEEN 



THE LINES a AND C IN 



FIG. 60 SHOWS Two 

 GASTRIC GLANDS. X 

 250. Diagrammatic 



a, Mouth of gastric 

 gland ; e, columnar 

 epithelial cells on 

 the food surface of 

 the stomach ; /, lu- 

 men of a gland; o, 

 oxyntic or acid cell. 



II 



